Although a substantial literature is developing regarding the effects of stress on decision-making (cf. Mather & Lighthall, 2012), the literature on stress and social decision-making is still in the beginning stage. The present research extends this new literature by examining the mediating and moderating factors of the effect of stress on social decision-making. Furthermore, a novel aspect of the research is its effort to connect the information-processing and functional perspectives, with regard to the acute stress response. Dual-mode theories state that emotional processing, relative to cognitive processing, occurs early during information processing (Murphy & Zajonc, 1993) and is associated with stimulus-driven behaviors (Mischel & Metcalfe, 1999). Therefore, an intensification of emotional processing and inhibition of cognitive control processes may lead to an earlier and more stimulus-driven initiation of behavioral responses than under normal circumstances. Moreover, such quick, automatic behavioral responses to environmental stimuli may be particularly useful during an acute stress response in that such responses could help prevent disturbances to homeostasis (Nesse, 2005). In order to facilitate such quick, automatic behavioral responses, emotional processing may be intensified and cognitive processing inhibited, during an acute stress response. In support of this notion, empirical findings show that acute stress increases emotion-related phenomena, such as reward salience (cf. Mather & Lighthall, 2012) and emotional learning (Luethi, Meier, & Sandi, 2008). However, in a social decision-making context, such enhancement of emotional processing may negatively affect the social interactions, such that negative emotions from perceived unfairness may be amplified when people are undergoing an acute stress response. More specifically, in the context of an Ultimatum Game, people who are stressed may reject more unfair offers than people under normal conditions. This research tested this main hypothesis, and examined emotions and trait emotion regulation tendencies as mediating and moderating factors, respectively, of the relationship between acute stress and Ultimatum Game rejections. These arguments are elaborated in Chapters 1, 2, and 3 of this dissertation. In two experiments, participants played the Ultimatum Game as the Responder after completing a stress or control task. The Cold Pressor Test was used as the stress induction method. Before and after the Ultimatum Game, participants completed state emotion ratings as well as trait emotion regulation questionnaires. Results from Experiment 1 showed a successful stress induction, indicated by higher cortisol levels in the stress, relative to control, group. Moreover, Experiment 1 revealed a significant Stress x Amount interaction, with stress having an effect on rejections of unfair offers, in comparison to fair offers. However, the emotion and emotion regulation results did not indicate the expected pattern, with emotions being uncorrelated with fair, nor unfair offers, and emotion regulation being associated with reduced rejections of fair, but not unfair, offers. In Experiment 2, an experimental manipulation designed to influence negative emotions, namely partner type, was employed. Results did not replicate the results of the first experiment, but unexpected results were found involving partner type and negative emotions, namely that participants who played with human partners, relative to those who played with computer partners, rejected more unfair offers and that negative emotions were positively correlated with rejections of fair and unfair offers. The experiments and their results are described in Chapter 4. It is difficult to draw firm conclusions from these results, but they do offer a starting point for interesting future research questions. Chapter 5 discusses some implications as well as limitations of the present research.